958the r bonding in the P-N and Se-N systems is important in stabilizing the low-energy conformer. This A bonding together with the electrostatic interaction is responsible for the high stability of the tub structure.Abstract: Carboxylate and carboxamide ligands on dirhodium(I1) catalysts can provide enormous regiocontrol in carbon-hydrogen insertion reactions of diazoasetate esters. Whereas 2,3,4-trimethyl-3-pentyl diazoacetoacetate (1) forms y-lactone products from insertion into primary and tertiary C-H bonds in a statistical distribution (61:39) with dirhodium(I1) tetrakis(perfluorobutyrate), only tertiary C-H insertion is observed with dirhodium( 11) tetraacetamide. Similar results are obtained with 2-methyl-2-octyl diazoacetoacetate (3), where competition for insertion exists between secondary and primary C-H bonds and electronic factors govern regioselection. However, with 2-methyl-3-isopropyl-3-heptyl diazoacetoacetate (2) and 2-methyl-1-phenyl-2-propyl diazoacetoacetate (4), product distributions from C-H insertion are invariant with the dirhodium(I1) ligands; insertion into a secondary C-H bond is favored over tertiary C-H insertion with 2 (95:5), and insertion into a primary C-H bond is preferred to benzylic secondary C-H insertion with 4 (70:30). In such cases, which are amenable to analyses by MM2 calculations, regioselectivity is determined by conformational preferences for which C-H insertion selectivity can be as random as that found with 2 and 4. When only one C-H bond site is available for insertion to form a five-membered ring product, only one y-lactone is observed from reactions catalyzed by dirhodium(I1) tetraacetate, and that product is not necessarily the one predicted by presumed electronic preferences.
The catalytic effectiveness of rhodium(II) acetate and hexadecacarbonylhexarhodium for ylide generation in reactions of diazo compounds with allyl methyl sulfide, representative allylic tertiary amines, and allyl halides is described. Exclusive formation of products derived from the [2,3] sigmatropic rearrangement of ylide intermediates generated from ethyl diazoacetate and allyl sulfides, amines, or iodides is observed. Cyclopropanation is dominant in reactions of either diethyl diazomalonate or ethyl diazoacetate with allyl chloride, and competition between cyclopropanation and ylide rearrangement is exhibited in reactions with allyl bromide. Allyl iodide
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